The present invention relates to a ball/wedge process in which a bonding or superfine wire made of copper is bonded to a semiconductor silicon chip; suitable superfine and bonding wires made of copper which are suitable for electrical connections for semiconductors; process for their manufacture and their use with semiconductors.
According to G. G. Harman, “Wire Bonding in Microelectronics”, McGraw-Hill 1997, pp. 1-10, pp. 67ff and pp. 203ff, in the ball/wedge process the bonding or superfine wire is bonded to a chip using a flamed ball, which is also referred to as a free-air ball (FAB).
Bonding wires are the connecting lines to electronic semiconductor elements, such as IC processors or sensors. Semiconductor components have so-called contact pads, which can also be called bonding patches. Bonding wires preferably have a spherical broadening at one of their ends, with which the bonding or superfine wire is pressed onto the contact pad and welded in the pressed state, usually supported by ultrasound (US). The other end of the bonding or superfine wire is preferably flattened in a wedge shape after previous US-supported pressure loading. The resulting bond connection is called a stitch or wedge bond.
Bonding and superfine wires usually consist of gold, although this has poorer electrical and mechanical properties in comparison with copper or silver. The reason for this is the tarnishing property of copper, which loses its bonding capability in a short time. It is possible to store copper bonding wire under a protective gas in order to prevent tarnishing. Silver interferes with many processes and applications in the semiconductor industry and is therefore to be avoided.
For cost savings relative to gold wires, U.S. patent application publication US 2003/0113574 A1 describes gold-jacketed silver or palladium wires. Copper-gold alloys are characterized by distinctly increased hardness relative to both metals. However, this hardness is undesirable for bonding wires, since the semiconductor can be damaged by pressing the bonding or superfine wire onto the contact patches of the semiconductor. Gold-copper alloys on copper wires can lead to cracks in the silicon chip during pressing onto the contact patches.